JP2680123B2 - Switching regulator power supply circuit - Google Patents

Description

The present invention relates to a switching regulator power supply circuit.

[Conventional technology]

FIG. 2 is a circuit diagram showing a conventional switching regulator.

In the figure, C1 is a smoothing capacitor for smoothing the input voltage (pulsating current), R1 is a resistor, C2 is a capacitor, and IC is
Control circuit with VIN terminal, GND terminal and drive terminal, T is a transformer, Q is a switching transistor, D2 and D3 are diodes, C4 is a smoothing capacitor, and a resistor.
The starting circuit is composed of R1 and capacitor C2.

When the input voltage is applied, the VIN terminal is applied between the VIN terminal and the GND terminal of the control circuit IC via the startup circuit (R1, C2), and when it reaches the operation start voltage, the control circuit IC The oscillation operation is started to generate a pulsed ON / OFF output from the drive terminal, and the pulsed ON / OFF output is supplied to the base of the transistor Q. Then, the transistor Q performs an on / off switching operation and outputs an output voltage from the secondary side of the transformer T. Since the voltage is supplied to the VIN terminal of the control circuit IC from the emitter of the transistor Q via the winding W1 and the diode D3, the control circuit IC continues to operate.

As a document describing this type of technique, Japanese Patent Laid-Open No.
No. -24405 Public information can be cited.

[Problems to be solved by the invention]

Now, in the switching regulator as shown in FIG. 2, when the input voltage that has been applied until then is cut off at a certain time, as shown in (A) of FIG. 2A,
The power supply terminal voltage (VIN voltage) of the control circuit IC is shown in Figure 2A (b).
The control circuit IC stops oscillating when the voltage drops to the operation stop voltage (see FIG. 2A (c)). Then, due to the discharge from the input-side smoothing capacitor C1, the power supply terminal voltage (VIN terminal) of the control circuit IC starts to rise as shown in FIG. 2A (b). Thus, when the VIN voltage reaches the operation start voltage, the control circuit IC starts oscillating again, discharges the charge on the input side smoothing capacitor C1, and the voltage starts to decrease.
The power supply voltage (VIN voltage) of the IC also drops again. After this, the discharge from the input side smoothing capacitor C1 starts again,
The oscillation of the control circuit IC was repeatedly started and stopped. This repetition is due to the hysteresis characteristics of the operation start voltage and the operation stop voltage of the VIN voltage of the control circuit IC, and operates as shown in FIG. 2A.

This repetition is repeated until the voltage of the input side smoothing capacitor C1 becomes the operation stop voltage of the power supply terminal VIN of the control circuit IC. Such repetition of oscillation and stop causes noise and is not preferable.

An object of the present invention is to provide a switching regulator power supply circuit that can avoid the above-mentioned repeated oscillation / stop operation or reduce the number of times of this repeated operation.

[Means for solving the problem]

To achieve the above purpose, after disconnecting the input voltage, an additional circuit is provided to supply a voltage to the power supply VIN terminal of the control circuit IC, sustain oscillation, discharge the input side smoothing capacitor all at once, and quickly Reduce the voltage.

[Action]

When the input voltage is applied, the additional circuit provided to achieve the purpose does not act on the control circuit IC or the like and operates normally. The operation is started only after the input voltage is cut off, and the voltage is supplied to the power supply VIN terminal of the control circuit IC.

By this operation, the control circuit IC continues the oscillating operation and continuously discharges the electric charge of the input-side smoothing capacitor.

〔Example〕

FIG. 1 is a circuit diagram showing one embodiment of the present invention. In the figure, the same components as those in FIG. 2 are designated by the same reference numerals. In addition, R2 is an auxiliary power supply charging resistor, D1 is an auxiliary diode, and C3 is an auxiliary power supply capacitor, which is different from the conventional circuit in that an additional circuit 1 including this is connected.

FIG. 1A is a waveform diagram showing voltage waveforms at various points in the circuit of FIG.

The circuit operation related to the present invention will be described with reference to FIGS. 1 and 1A.

The control circuit IC starts oscillation when the voltage charged in the IC power supply smoothing capacitor C2 via the IC starting resistor R1 after the input voltage is applied reaches the oscillation start voltage at the VIN terminal. In addition to the main charging route, electric charges are stored in the auxiliary power supply capacitor C3 via the auxiliary power supply charging resistor R2.

When the control circuit IC oscillates, the switching transistor Q is turned on and off, and the voltage rectified by the rectifying diode D2 and the rectifying capacitor C4 is output via the switching transformer T. Also, the diode D3 allows the power supply terminal VI of the IC.
Supply voltage to N.

As shown in Figure 1A (a), when the input voltage is cut off, the voltage supplied from the diode D3 to the VIN terminal decreases, and the power supply terminal VIN voltage of the control circuit IC is seen in Figure 1A (b). However, since the voltage is supplied from the auxiliary power source capacitor C3 through the auxiliary diode D1, the control circuit IC continues to oscillate. Due to the continuation of this oscillation, the electric charge of the input side smoothing capacitor C1 is discharged through the control circuit IC.

Here, the capacity of the power supply rectifying capacitor C2 is determined so that the operation rising after the input voltage is applied can be freely set.

Contrasting FIG. 1A with FIG. 2A, the control circuit according to the present invention
It will be appreciated that after the input voltage is cut off, the input side smoothing capacitor C1 is fully discharged and the VIN voltage reaches the operation stop voltage without disconnection operation, and it will be recognized that the IC continuously operates.

〔The invention's effect〕

According to the present invention, the oscillation of the control circuit IC after the input voltage is cut off without delaying the startup of the operation when the input voltage is applied.
Repeated stop operations can be avoided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG.
FIG. 2 is a waveform diagram showing voltage waveforms at various parts in the circuit shown in FIG. 2, FIG. 2 is a circuit diagram showing a conventional circuit of a switching regulator, and FIG.
FIG. 2A is a waveform diagram showing voltage waveforms at various points in the circuit of FIG. Explanation of symbols 1 ... Additional circuit, R2 ... Auxiliary power supply charging resistor, D1 ... Auxiliary diode, C3 ... Auxiliary power supply capacitor.

Claims (1)

(57) [Claims] 1. A control circuit having a VIN terminal, a GND terminal and a drive terminal, a transformer and an input side DC voltage supplied via a smoothing capacitor (CI) is applied to the primary side of the transformer. A switching transistor that outputs an output voltage from the secondary side of the transformer by switching on and off, and the input side DC voltage between the VIN terminal and the GND terminal via a starter circuit (R1, C2). A switching regulator comprising: a control circuit for supplying an ON / OFF drive output from the drive terminal to the transistor to perform ON / OFF switching operation when applied between the input terminal DC voltage The charge stored in the smoothing capacitor (C1) up to that point is discharged from the VIN terminal to the GND terminal of the control circuit when the operation is stopped.
And a second discharge path from the VIN terminal of the control circuit through the drive terminal to the ground via the switching transistor and finally to the control circuit without interruption. Auxiliary power supply capacitor circuit (R2, R2, which continuously supplies the charge between the VIN terminal and the GND terminal of the control circuit to sustain the operation of the control circuit and the switching transistor until a voltage at which the operation is stopped is reached. Switching regulator power supply circuit characterized by having C3, D1).